Recently, attention has paid to a semiconductor device called a “substrate with a built-in chip” in which a individually divided LSI chip and the like are buried in a substrate made of resin and the like and a semiconductor device in which an insulating resin layer and a wiring layer are formed on an LSI chip. In semiconductor devices such as a substrate with a built-in chip, it is necessary to bury a chip in a substrate made of resin and the like, then laminate an insulating layer over the substrate, and further form a via hole through the insulating layer to electrically connect an electrode pad on the chip to an external electric terminal and the like.
An example of a method for forming a via hole through an insulating layer includes a method for forming an insulating layer made of a photosensitive resin on a substrate with a built-in chip, exposing the photosensitive resin to light, and developing the photosensitive resin to form a via hole. The mechanical strength of a photosensitive resin is, however, typically so low that the device is often disadvantageously unreliable. Further, many sheet-shaped resin materials used to form the insulating layer are nonphotosensitive resins. Since photosensitive resins are not produced in volume, the use of a photosensitive resin disadvantageously increases the cost.
On the other hand, nonphotosensitive resins are frequently used as sheet-shaped insulating materials used in printed wiring boards and the like. Nonphotosensitive resins are therefore produced in volume, and the use of a nonphotosensitive resin can reduce the cost. When a nonphotosensitive resin is used to form an insulating layer in a semiconductor device with a built-in chip, however, there is a problem of how to form a via hole.
That is, when a nonphotosensitive resin is used, a via hole is typically formed by using a laser beam. In this case, a laser beam passes through the insulating layer made of a nonphotosensitive resin, and an electrode pad located under the insulating layer and made of Al and the like is flied apart by irradiation of the laser beam. As a result, the device including a semiconductor chip is disadvantageously damaged.
To solve such a problem, in the printed wiring technology disclosed in Japanese Patent Laid-Open No. 2003-7896 (FIG. 6), transition layer (A) is provided as a laser stopper layer. The transition layer is comprised of at least two metal layers (33, 36, and 37) and larger than die pad (24) of IC chip (20), which is a semiconductor element. The technology described in Japanese Patent Laid-Open No. 2003-7896 thus allows a laser beam to form a via hole without damage to the die pad (paragraph number (0009)).
On the other hand, in the printed wiring technology described in Japanese Patent Laid-Open No. 2005-332887, stud bump 105 is formed on electrode pad 104 on chip 101, and insulating layer 109 made of epoxy and the like is laminated over the stud bump. A laser machining is then performed to form via hole 110 that reaches the stud bump (FIG. 7).
In this technology, since stud bump 105 serves as a stopper layer in the laser machining, electrode pad 104 will not be directly irradiated with the laser beam. Therefore, the electrode pad is not flied apart by the laser beam, or the device including a semiconductor chip is not damaged (paragraph numbers (0022) and (0062)).